Influence of emulsified fuel combustion on soot formation process

点击翻译按钮获取中文摘要

It is difficult to achieve simultaneous reductions in soot and nitrogen oxides (Nox) emitted from diesel engines because of the trade-off relation. Water addition is effective to reduce Nox emissions without deterioration in the combustion performance. It is unclear, however, how the water addition influences the soot and particulate emissions. First, experiments were carried out to determine the formation characteristics of smoke emissions using actual diesel engines fueled with water-in-oil emulsified fuels. The experimental parameters with two types of base fuel (gas oil and biodiesel, fuel transesterified from vegetable oil), EGR (exhaust gas recirculation), and water addition were investigated. Compared with water free fuels, the smoke density of the emulsified fuels reduced remarkably at all operating conditions.To examine the formation process of particulate, experiments using a model chamber were made. It is possible to simulate diesel combustion and a model chamber simulating constant volume combustion was employed. The experimental apparatus consisted of five parts : a modified combustion chamber of the diesel engine, a vessel for high temperature and high pressure air, a rupture system with a needle cutter driven by a solenoid, a vessel to contain expanded gas, and a system for single injections of diesel fuel. A thin steel plate is used to partition the combustion chamber and the gas expansion vessel. In the combustion process the thin plate is ruptured by the needle cutter and the combustion reaction stops immediately, because the burnt gas expands in an extremely short time. The preliminary combustion experiments were conducted at atmospheric conditions with an initial air pressure of 2MPa and 450℃, and the ignition delay was longer than with actual engines. The apparatus will need improvements to obtain more precise data.